How To Ship Flats With Stamps.com_BlogIf you need to send a manuscript, set of reports, or sheaf of bills, you’re going to need something a bit larger than a normal letter-sized envelope. The USPS recognizes a category of Flats which can comfortably house numerous sheets of paper, magazines, journals, books or other material, without needing to fold the items.

The key thing to remember is that flats must always be flexible and uniformly even and smooth with no large bumps.  Are you sending a license plate in an envelope?  Is your envelope wrapped so tightly in plastic that it can’t even bend anymore?  Are you sending a box or parcel?  Then none of these mailpieces would be considered flats.

The USPS maintains a consisting standard to determine whether something is considered flexible or not.  The official “flexibility test” states that a mailpiece is considered flexible “if both ends can bend at least 1 inch vertically without being damaged.”  The USPS has a useful guide that shows you how you can perform your own Flex Test.

The official definition of a flat is that it must have a minimum height of 6-1/8″ and a maximum height of 12″, and a minimum length of 11-1/2″ and a maximum length of 15″.  The minimum thickness is ¼” and the maximum thickness is ¾”.  Anything exceeding these measurements will be bumped up to the next mailpiece of Thick Envelope/Parcel.

Besides the standards by which there is a minimum and maximum thickness for flats, there are two other regulations to consider:

– The ¼ Protuberance Rule
¾ of an inch thick is the maximum thickness for flats, but keep in mind that there is an additional and separate regulation regarding uniform thickness.  Your flat has to be uniformly thick, so it can’t have any bumps, protrusions, or bulges that cause more than a ¼-inch variance in thickness.  Even if your flat is less than ¾ inch thick, it may not always be a flat.  If it contains an item inside of it that is creating a bump that is more than ¼ inch thick, then the mailpiece would not be considered a flat.  Therefore, the key thing to prevent is from the mailpiece becoming nonuniformly thick with bumps, bulges, lumps, and prominences.

– Content Shifting
Because of these thickness and protuberance rules, flats are best used for sending documents, but if you want to use flats for non-paper contents, you should secure the items to prevent shifting.  This is because there is an additional postal rule that states that non-paper contents cannot move inside the flat to such a degree that they would create a bump or protrusion, or cause the items to burst out of the flat.  The official maximum for content shifting is 2 inches, so your items cannot move inside the flat for more than that distance.    

Sending Flats With makes it easy to send to flats!  You can print postage for flats in a number of different ways depending on how much information you want on your label.

#1. Need just a stamp? 
In your software, select “Stamps” on the left side of the screen and then select “Large Envelopes and Flats” under the drop-down Mailpiece menu.  You can then select your mail class as First Class (up to 13 oz.).

#2. Want to print postage for a Flat with the delivery and return addresses included? 
In your software, select “Envelopes” on the left side of the screen and then select “Large Envelopes and Flats” under the drop-down Mailpiece menu.  You can print to a wide variety of labels, such as SDC-3110 or Avery labels like Avery 32403.

#3. Printing First Class, Priority Mail and Priority Mail Express Shipping Labels for Flats?
Find these mail class options under the “Packages” option on the left side of the screen.  Just look for the mailpiece called “Large Envelope/Flat.”  These can be printed on plain paper, labels such as the SDC-1200, or Avery labels like Avery 32402.   Tracking is available for Priority and Priority Express Shipping Labels for Flats.

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